E46Fanatics - View Single Post - 330 ->325xi brake swap and rear brake question
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Old 02-26-2012, 09:05 PM   #9
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See below on this one.

Originally Posted by jgold47 View Post
Thats a fair question, but I disagree with sam's assessment that their is no DD benefit. I only learned about this swap this morning, so based on what I have been able to ascertain, I have two schools of thought on it.

First, I want to clarify that I only plan on doing this to the front. I need to get new pads and rotors anyways, so I am only paying for new carriers and calipers. I can buy a set from NAPA (for example) for 200 for the pair, so this is only costing me a small amount of money.

Now as to the reasoning:

1. why did BMW put bigger brakes on the 330's? The car is not significantly 'sportier' (not in an xi trim anyways). Its not significantly heavier either. The only reason I can see is because it represents an 'upgrade'. Bigger is better in brakes, that shoudnt be in dispute. What is in dispute is if the 325 brakes are inadequate (they are not), but you could argue that about any number of modifications that people make to their vehicles (whats wrong with the stock clutch, oem tires, oem shifter, etc....)
Yes, bigger is better and larger brakes will make a difference...but not in daily driving. It's just like putting in SS brake lines and expecting a difference. In race conditions, bigger brakes are better because they shed heat faster. Also, adding weight to the brake rotor/calipers/carriers is unsprung weight which is much worse than sprung weight. I'm not sure what the exact weight difference is but remember to multiply by two for the front and two for the rear. I could, and do, argue that a number of mods that people make to their street cars are pointless. That's why mine is 100% bone stock other than the suspension, something that does actually make a noticeable difference in daily driving. Also, the examples of upgrades that you noted are all upgrades that can and will be obvious and beneficial during daily driving.

that brings me to my reason:

2. I do mostly stop and go driving with the occasional rip out in the countryside. I had pretty bad brake fade the last time I did this, which is why I am doing new pads/rotors (regardless). I also am pretty hard on my brakes, when I learned to drive stick, I didnt really cotton to downshifting into stops, so I use my brakes quite a bit to stop the car, so again bigger is always better.
If you are experiencing fade in normal daily conditions, you need new rotors and pads bad. I think you already know that. With new rotors and pads, even the 325 ones, you won't notice fade in daily driving conditions. Within legal limits at least. Also, I think you might be interpreting brake fade for reduction in pedal pressure due to air and/or moisture in your brake lines. As Kubica said, try to change out your brake fluid for some fresh stuff and see if that helps out. I do the same thing as you, brake and not downshift unless I'm entering a turn. New brake pads/rotors are cheaper than new synchros.

And my last reason, because I am pretty much dead set on turning my base level xi into a car its not. Upgraded to style 44's, gauge cluster rings, lip spoiler, etc... maybe it will get mistaken for a zhp some day
No arguement here, the bigger brakes do look cooler in the rims.
Originally Posted by redbull 325is View Post
Disagree. It's not because you can break the static friction of your tires that your brakes are adequate. If you modulate your brakes properly you won't lock up the wheels and stop much quicker. This practice causes a lot of energy to be transferred into heat, a place where as you mentioned, larger brakes are useful.
I won't disagree with the fact that modulating your brakes will get you a faster stop and will also cause your rotors to heat up much more. BUT how often do you make repeated panic/hard stops from high speed in rapid succession when you drive on the road? If you do it more than two or three times in a row, you are being an idiot and reckless. Also, if you can break the static friction between the tires and the road, that does mean your brakes are adequate and that your tires are then the weak link in the chain. Also, when you are modulating the brakes, you are not using the full clamping force of the brake calipers.

Originally Posted by White_Knuckles View Post
So given the cars are essentially the same weight (330/325 XI's), the larger front only setup would make for less fade when whipping and spurring in the twisty's as well less fade when hard braking under a panic stop. I thought ABS took over modulation under panic situations? Red, do you suggest pedal application or human modulation is applied as normal? Of course we don't generally mash the pedal on but when digging into them, it's normally progressive with slight on/off unless your performing winter techniques such as braking on ice staying out of ABS land.

Bigger sounds better if you can use it. I see guys putting on those "big brake kits" and always thought for the thousands they spend, the street pay-off was iffy?
The brakes won't be any different during panic stops unless you are performing them repeatedly in rapid succession. They also won't be any different unless you are tracking the car. On the road, you should never be seeing speeds and subsequent repeated rapid deceleration that cause brake fade. If you are tracking then it's a different story. Again, when your tires lock up it'll be up to the ABS and the adhesion of your tires to the road that will make you stop better/faster unless you are experienced and aware enough to modulate the brakes yourself. Under panic situations, the ABS will take over. The average person is not aware enough to modulate the brakes while under pressure. Remember though that the main function of ABS is not to make you stop faster but to help you maintain control and to enable avoidance during stopping. IMO, most people who install big brake kits are doing it mostly for the looks.

FWIW, I don't really have any personal investment in whether or not you install the 330 brakes. It's your car and your money, I'm just laying out the facts and my opinions.

Last edited by SamDoe1; 02-26-2012 at 09:10 PM.
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